Tear-resistant porous plastic sheet material comprising polyvinylchloride and a copolymer of butadiene-acrylonitrile



United States Patent TEAR-RE'SISTANT POROUS PLASTIC SHEET MA- TERIALCOMPRISING- POLYVINYLCHLORIDE @1512 lrIalE'COPOLY MER OFBU'IADIENE-A'CRYLO- Orville N. Foust, Melrose, and Eugene G. Seems,Beverly, Mass assignors to United Shoe Machinery Corporation,Flenungton, N. J., a corporation of New Jersey No. Drawing. ApplicationApril 26, 1952, Serial No. 284,637

1- Claim. (CL- 260-25) This invention relates to plastic sheet materialand more particularly to improved. resinous polymeric material in the.form of micro-porous, tear-resistant sheets suitable for use infootwear, the material being particularly. advantageous in the making ofinsoles.

A portion of the present disclosure is presented in the application forUnited States Letters Patent, Serial No. 41,726, filed July 30, 1948 inapplicants names and now abandoned.

Many materials have been considered and tested for use as insolematerials in footwear. Leather has been satisfactory in such use andheretofore has been much preferred by many users but this preferredmaterial is commonly known and understood to possess somecharacteristics which detract from its desirability. Leatherdeteriorates rapidly when subjected to the effects ofmoisture'andfootperspiration. Its resilience is not sufificient to giveproper or'preferreclcushioning beneath the foot of a wearer:Fabricat'ed'fibrous materials have also been usedand with success. Inmany cases fibrous materials have been found'prefera'bl'e overleatherfor insole use buthere again the'mat'eri'a'ls donotcompletely'satisfy the requirements of what is desired" to giveoptimum satisfaction and increased comfort to the wearer.

Recently it has been. determined that synthetic, resinous, polymeric.materials including. at least one vinyl resin, when properly sinteredfrom an initial powder or particle form into integral micro-poroussheets, provide a resilient structure wihch is far. superior to leatherand fibrous materials in so far as. insole use. is concerned. Thissuperiority has been provenin extensive andpractical wear tests.Broadly, thetechnique of forming integral micro-porous plastic sheets istaught in the'U'nited'States Letters Patent No. 2,371,868, granted.March 20, 1945, to Herbert Berg and Martin Doriat. The porous material,assuming that a given shoe is of the. proper size, does not draw thefoot in any type of weather. It may be expected that the. sensation ofwearing rubber boots will be imparted to thewearer in the use of thismaterial but wear tests have shown that the porous plastic insoles areactually cool in summer and are comfortably warrnin winter. Moisture, ingeneral use of the tested insoles, is adequately transferred-from thefoot and this characteristic of. the plastic structure-together with theresilient. support. thelatter provides the foot gives comfort tov thewearer. heretofore not. experienced; This comfort is accompanied bysubstantial protection of the foot against localized pressuresoccasioned by small stones and so forth met with in walking or bycramped spots on the foot due to improper or imperfect fitting of theshoe. Other softer or equally soft materials could be used as insolematerial but the micro-porous plastic material herein contemplateddefinitely sustains or resiliently supports the foot without losingitsporosity or moisture transpiration characteristics either momentarily orpermanently.

Despite. the advantages of the porous plastic as an insole material,difficulty has been experienced in its use i because of its lack ofstrength in tear resistance especially when tension must be resisted orwhen stitching or sewing ofthe material is necessary or desirable.Sewing thread tends to pull or cut through the porous plastic andresistance of the porous polymeric material to such shearing or tearingby the thread has heretofore been negligible. The sintered products, asheretofore known, will crumble under the slightest strain such asinduced by the material being subjected to a slight twist, especially inthe absence of a plasticizer. With the plasticizerpresent, the materialis improved but still leaves much to be desired in so far as stability,resilience and resistance against tension and tearing forces areconcerned. As a result, the use of which is very much stronger (2 to 20times stronger dependent upon the specific formulation) in so far asrip-tear strength and resistance against tension stresses: areconcerned, this pronounced change in the physical characteristics notbeing accompanied by any objection-- able loss in porosity.

crease in porosity. In all cases the desired combination.

of porosity, flexibility, and resilience may be had withoutobjectionable rubberiness.

An object of the present'invention is to provide im-- provedmicro-porous plastic sheet material for insoles, which material combinesa high degree of porosity,

proper firmness and resilience together with greatly increased'tensionand tear strength.

The term .micro-porous is used herem 'to define a material having pores.so small that they, are not easilypermit the:

discernible with the naked eye but which passage of air.

The customary definition of the word sinter. as used hereinafter is asfollows: To become or cause to. become a coherent solid mass by heatingwithout thoroughly melting. This meaning. is adhered to herein but'it isto beunderstood that the process disclosed and claimed is notsuch astosecure a solid or'non'-porous.product i. e.although a sinteringtemperature is used, the pres sure, temperature and time condition arecontrolled and are not imposed to such an extent as to solidify theparticles into a mass of non-porous material.

In' theproduction of the improved sheet material an intimate mixture of.compatible thermoplastic polymers including at least one vinyl resin isblended and subsequently made into a powder each particle of which ismade up of the blended polymers. A layer of such particles' or powder isthen sintered together with interstices being maintained between theparticles yet'with the latter so joined as to form a unitary article.,The preferred resins are solid water insoluble non-tacky resins derivedby polymerization of vinyl chloride or' copolymerization of 195 to 99.5%of vinyl chloride with vinyl acetate monomers. These. vinyl resins maybe combined with from'about to about of the weight of th'e'resin of acopolymer of butadiene and acrylonitrile in the ratio of from about 33to 40 parts of acrylonitrile to 67 to 60 parts-of butadiene.

The. ingredients may contain a vulcanization agent, a filler, and anaccelerator. Duringthe process of sintering, the ,resins,.to someextent,.must be'thermoplastic and compatible. A thermoset resin may beadded, however, and this would act as a type of filler.

A mere. mixture of particles of several. compatible p'olym'e'rs-i.e.one-polymer only'in each"particle will In some. cases the increase in:strength is accompaniedv by a definite and substantial in-- not serve inthe present invention. It is essential, if the necessary characteristicsare to be secured in the sintered product, that each particle of thepowder to be sintered be made up of a polymeric blend comprising atleast one of the polymeric resins as set forth above.

In preparing the blend of resins a solid or liquid plasticizer is used.If a solid plasticizer is employed, the ingredients may be fluxed on ahot two-roll rubber mill. The resultant sheet is chilled, coarselysubdivided and then ground to a fine powder. If the plasticizer selectedis a liquid, the latter may be stirred together With the resin or resinsat some temperature below the fusion point and the product issubsequently finely subdivided. Another way of obtaining a sufiicientlyintimate mixture of the resins is by precipitation of the polymers froma colloidal dispersion of them and with a subsequently division intofine particles.

In sintering a given layer of the plastic particles heat is appliedduring the pressure molding process and this heat may be derived fromheated platens of a press or by high frequency heating. Heat appliedfrom an outside source (heated platens) results in satisfactorysintering and increased tear and tension resistance in utilizing thepresent invention but high frequency heating is preferred as eachparticle is heated outwardly to its surface and to the surface of thesheet or article giving a uniform heating effect emanating from withinand becoming definitely effective throughout the layer of particles and,in many cases, resulting in greater tear and tension resistance (withoutloss in porosity) as compared with the results secured by other methodsof heating.

The following two examples A and B are given by way of illustration ofwhat is to be expected in respect to porosity and tear strengthcharacteristics of porous plastics as heretofore known-i. e.--prior tothe present invention:

Example A (one resin) Ingredients: Parts by Weight VYNY 66.46 Methox29.20 VIN 2.20 Pigment 2.34

The VYNY is a copolymer comprising 97% to 99.5% by weight of vinylchloride and 3% to 0.5% by weight of vinyl acetate and is produced bythe Carbide and Carbon Chemicals Corp. of New York, N. Y.

Methox is di-methoxy ethyl phthalatea plasticizer made by the Ohio-Apex,Inc., of Nitro, West Virgina.

The VIN is strontium octoate. It is a stabilizer product of AdvancedSolvents and Chemical Corp. of New York, N. Y.

The above ingredients, intimately mixed and placed in the form of a finepowder as a layer .25 inch deep within a mold, is compressed to athickness of .125 inch and sintered (using steam-heated platens) at atemperature of 132 C. After cooling and removal from the mold, theresultant sheet is porous (40 c.c./in. /sec.) but its tear strength isonly 28 (lbs./ inch of thickness).

A duplication of the use of this example may not result in a product ofthe same porosity as it is difficult to make consecutive sheetsidentical. The figures as to porosity and tear strength are to be takenas merely illustrative in a general sense and as what may well beexpected in a specific sense and this holds true in all the followingexamples.

Example B (one resin) The VYNY is a resin copolymer comprising 95% byweight of vinyl chloride and 5% by weight of vinyl acetate and isproduced by the Carbide and Carbon Chemicals Corporation of New York, N.Y.

The above ingredients are mixed, compressed and sintered as in ExampleA. The cooled resultant sheet has a porosity of 13 (cc. of air lu /sec.)and a tear strength of 12 (lbs./ inch of thickness).

The present invention is illustrated by the following examples whichdemonstrate not a mere difference in degree of strength in the novelporous plastic but a multiplication thereof. The ingredients areintimately blended in conventional ways prior to the reduction of theblend into fine particles.

Example 1 (resin blend) Ingredients: Parts by weight VYNY 125. HycarOR-15 94. Methox 15. Calcium stearate 2.5 VIN 3.75

Example 2 (resin blend) Ingredients: Parts by weight Polyblend 500x479100. Hycar OR-15 28. Calcium stearate 2.0 Methox 3.0 Sulphur 2.0 Captax1.7 Agerite Stalite 2.3 Altax 1.0

The Polyblend is a colloidal blend (not fluid) produced by the B. F.Goodrich Company and is composed of 70% polyvinyl chloride and 30% HycarOR15.

The Captax is mercaptobenzothiazole. It is a rubber accelerator producedby the R. T. Vanderbilt Co.

Agerite Stalite is heptylatcd diphenylamine, also a product of the R. T.Vanderbilt Co.

Altax is benzothiazyl disu1fide-a rubber accelerator made by the R. T.Vanderbilt Co.

A milled mixture of the above ingredients is chilled and subdivided intosmall particles a layer of which is slightly compressed and sinteredinto a micro-porous sheet with the use of high-frequency heat. Theporosity is found to be (40 c. c. of air/inF/sec.) and the tear strengthis 126 (lbs./ inch of thickness).

Example 3 (resin blend) Ingredients: Parts by weigh QYNA 50. Hycar OR-2550. Vanstay 1.8 Acrawax C 5. Pigment 1.8

pany, Inc. of Brooklyn, N. Y. The Acrawax gives an improved surfaceappearance and helps to improve surface slip.

Particles of a milled mixture of the above are sintered, usinghigh-frequency heat, into an integral sheet having a porosity of 40 (c.c. of air/in. /sec.) and a tear strength of 114 (lbs/inch of thickness).

Example 4 (resin blend) Particles, each of which is composed of the sameingredients as used in Example 3 above, are sintered into a sheet with aslightly increased pressure. The resultant sheet has a reduced porosityof 8.5 (c. c. of air/in. sec.) Which, nevertheless, is far superior toleather and a tear strength of 264 lbs/inch which is surprisingly highfor porous plastic material.

The novel materials, formed by the method of the present invention, arestable and, rather than easily tearing or crumbling when subject totension or stitching stresses, demonstrate such improved characteristicsthat they may successfully be used in the making of insoles forfootwear. For insole wear in particular an improved combination ofporosity, flexibility and weight-sustaining power may be had Withoutobjectionable rubberiness.

Having fully described our invention, What we claim as new and desire tosecure by Letters Patent of the United States is:

A flexible micro-porous sheet suitable for insoles and having sufiicientfirmness to sustain the weight of a wearer without compacting, andsubstantial tear resistance and strength in tension, said sheetcomprising sintered together fine particles of polymeric materialcohesively joined with interstices between the sintered particlesforming continuous pores and the polymeric material in each of saidparticles comprising a vinyl chloride polymer resin from the groupconsisting of polyvinyl chloride and copolymers of vinyl chloride andvinyl acetate containing from 95% to 99.5% of vinyl chloride,plasticized with a rubbery copolymer of butadiene and acrylonitrileprepared from about 33% to about acrylonitrile and from about 67% toabout of butadiene, the weight of said rubbery copolymer being fromabout to of the weight of said resin.

References Cited in the file of this patent UNITED STATES PATENTS2,297,248 Rudolph Sept. 29, 1942 2,371,868 Berg et al. Mar. 20, 19452,452,999 Daly et al. Nov. 2, 1948 2,459,739 Groten et al. Jan. 18, 19492,465,493 Strickhouser Mar. 29, 1949 2,570,182 Daly et al. Oct. 9, 1951OTHER REFERENCES Rubber Age, April 1944, page 67.

Emmett: Ind. & Eng. Chem., August 1944, vol. 36, No. 8, pages 730-734.

Young et al.: Ind. and Eng. Chem., November 1947, vol. 39, No. 11, pages1446 to 1448.

